Can I Put You on Hold? I've got Zork on the Other Line

A guy named Simon Ditner has ported the classic text adventure, Zork, not to a game console but to the phone:

The crazy thing Ditner wanted to do was play Zork over the telephone.

Zork is a text-based adventure game that debuted in the late 1970s. It became a popular series in the early 1980s with versions for the IBM PC, Apple II and Commodore 64 systems. Ditner tried to take that game and make it playable over the phone using only your voice.

His effort is called Zoip (a hybrid of Zork VoIP). In order to build his phone-based game system, Ditner started with a stock Asterisk installation and then added a number of items to do speech recognition and text to speech.

In the game, the Zoip system reads out a Zork description using the Festival text-to-speech engine. For instance: "This is a small room with passages to the east & south. Bloodstains & deep scratches mar the walls."

What is a grue?